Window resizing still slow?

Why is window resizing still not 60 FPS in the vast majority of situations in Yosemite? I can understand windows with lots of reflowable content, but even simple windows can sometimes chug. Not to mention, changing between tabs on the "About This Mac" screen still isn't butter smooth on the nMP.

To be clear, I really do want to learn the technical reason behind this. Windows doesn't have this issue to the same extent; most windows resize as smooth as the mouse pointer can move. What is OS X doing differently?

Yeah, it's not a big deal but it seems inexplicable. It's really the only part of the OS with noticeable lag (at least, on non-Retina macs).